Stropharia caerulea, commonly known as the blue roundhead, is an inedible species of agaric fungus in the family Strophariaceae. It is a common species found in Europe and North America, where it grows as a saprophyte in meadows, roadsides, hedgerows, gardens, and woodchip mulch. S. caerulea was officially described to science in 1979, although it was known to be a distinct species for about two centuries before that. The taxon Stropharia cyanea, as defined by R